In general, large containers all have four side plates and a base. The large containers for transporting liquids or bulk often further have an upper cover for protection of internally loaded cargo. The upper cover is enclosed by a circle edge guard, which is close to the outer side of four side plates of the container. When the cargo inside the container applies great force to the side plates, the edge guard of the upper cover can be a certain degree of protecting the side plate from too large deformation. In addition, when the liquids or the bulk inside the container fluctuates upward, the upper cover can well limit the ups and downs of the liner bag which contains the liquids or the bulk so as to protect the liner bag from damage. This requires the upper cover to reliably connect to the box upon using. In addition, most of four side plates of the large containers can be folded in turn to reduce occupied storage space when the container is not used, thereby reducing the product turnover and storage cost.
In the existing product, there is a locking mechanism for the box and upper cover, having a crossbar with a handle which is housed in a recess provided on the upper edge of the upper cover. The side of the recess has a hole, through which crossbar stretches into the recess in the side plate of the container. When the upper cover is in use, the crossbar restricts the upper cover from moving upward from the box, and at the meantime, the handle on the crossbar is restricted moving horizontally by the ribs in the recess, so that it can be locked reliably. Although this type of design satisfies the basic connection of the upper cover and the box, when the upper cover is placed on the box and the crossbar is in the extended station, the crossbar is pressed directly to the side plate of the box and thus may be damaged as the crossbar has no return structure.
The known disclosed patent 201110295197.2 also relates to a method of locking the upper cover and box. The upper cover is provided with a groove which can accommodate a reed with a resilient sheet, the tongue of the reed can pass through the hole in the side portion of the groove and stretch out to the recess on the inner side of the container side plate. Particularly, the tongue has a slope which has a technical effect that when the upper cover is placed on the container, the pressure applied to the cover will force it to be locked on the side plate rather than damage the tongue such as in the above solution. This solution reduces the specific operating action of locking the side plate, and avoids the damage of the relevant components on the upper cover, but because of its own thicker thickness and not directly above side plates, the groove cannot be well concealed by means of the structure of the bottom of the box when the product is folded, so that the height of the stack after folded is high, which is not conducive to transport while increase the cost of storage, and when the box loads full of the liquids, the side plate suffers pressure and expand outward, which leads the depth the tongue inserts into the recess of the side plate is so shallow that the reliability of the latch is greatly reduced.
The above solution of prior art also has a common drawback, that is upon unlocking, operator is required to go to the side plate where two latches are located respectively so as to operate unlocking respectively, which need heavy workload for the operator.